1. Field of the Invention
The present invention relates to a film defect inspection method for a film formed on a substrate, such as an electric charge generation layer, electric charge transport layer or undercoat layer formed on a relatively rough surface of a conductive substrate of an electrophotographic photoreceptor to be mounted in a digital copier or printer.
2. Description of the Related Art
A method for manufacturing an electrophotographic photoreceptor (hereinafter, also simply referred to as xe2x80x9cphotoreceptorxe2x80x9d) with a uniform film thickness and electric characteristics is disclosed in Japanese Unexamined Patent Publications JP-A 4-336540 (1992) and 6-130683 (1994). In this method the film thickness of an undercoat layer or electric charge transport layer formed on a conductive substrate (hereinafter referred to as xe2x80x9csubstratexe2x80x9d) of the photoreceptor is controlled and the amount of applied paint is adjusted.
Paints for the electric charge generation layer, electric charge transport layer, and undercoat layer are applied onto the substrate by a dip coating method which is particularly excellent in productivity among various methods. The dip coating method is accomplished by dipping the substrate in a tank filled with the paint, and subsequently raising the substrate therefrom at a constant speed. However, the organic solvent in the paint tends to evaporate, and variations in coating thickness tend to occur due to a change in viscosity of the paint.
The film thickness of each functional film of the photoreceptor is an important factor for determining the sensitivity, and should be severely controlled. Although examples of the film thickness measuring method include the contact type, non-contact type, and photograph type, the non-contact type whereby the coating itself will not be marred is preferable. The light interference method is particularly preferable because it is capable of measuring the film thickness of the layer containing no pigment such as the electric charge transport layer or undercoat layer. It is also excellent in accuracy of measurement and resolving power, and requires no particular facilities. In JP-A 4-336540 and JP-A 6-130683, the film thickness is successively measured by the light interference method, and the results of the measurement are fed back to automatically control the coating speed to an appropriate speed.
The variations in film thickness of each functional film of the photoreceptor also cause surface potential variations. The surface potential variations make it impossible to obtain a uniform half-tone image. Further, inclusion of foreign matters results in black points and white points occurring on the image. Therefore, defects such as variations in film thickness and inclusion of foreign matters need to be severely inspected.
The inspection of defects such as variations in film thickness or inclusion of foreign matters is also accomplished by the light interference method. Specifically, it is accomplished by the visual evaluation of the interference fringes occurring on the film surface when the film on the substrate is irradiated with light. In the case where irregularities or discontinuous portions occur in the interference fringes, it is judged that defects of some kind such as variations in film thickness and inclusion of foreign matters occur.
Such a film thickness measurement and defect inspection by the light interference method are possible for the lamination-type photoreceptor having a transparent film because interference of irradiation light occurs therein. However, it is impossible for the monolayer-type photoreceptor wherein electric charge generation substances such as pigment are dispersed in the film because the irradiation light is absorbed or scattered by the electric charge generation substances and hence undergoes no interference.
The light interference method cannot be directly applied to the film formed on the substrate whose surface is made relatively rough in order to control the light interference. In recent years, digital electrophotographic photoreceptor mounted in digital color copiers or printers have replaced analog electrophotographic photoreceptors. In the digital photoreceptor, the conductive substrate surface is subjected to a surface-roughening treatment in order to inhibit the interference fringes resulting from the light reflected from the substrate surface and the light reflected from the film surface. Thus, in the substrate whose surface is relatively rough, the rays of light from the substrate surface and the film surface are less likely to interfere with each other, and the rays of light are scattered. Accordingly, film thickness measurement and defect inspection by the light interference method are difficult.
Further, the clearer the interference fringes are, the more the accuracy of the defect inspection is improved. However, in the digital electrophotographic photoreceptor, the interference of light is less likely to occur due to the foregoing surface-roughening treatment, and hence the interference fringes become obscure. Accordingly, the inspection accuracy is reduced. Consequently, the load on the inspector increases, and thus the inspection time becomes longer, resulting in a reduction in productivity.
It is an object of the invention to provide a film defect inspection method for inspecting defects such as film thickness variations and inclusion of foreign matters of a film formed on a substrate whose surface is relatively rough, by the light interference method.
The invention provides a film defect inspection method for inspecting defects of a film formed on a substrate by a light interference method, comprising:
irradiating the substrate with light of a longer wavelength than a surface roughness Rmax of the substrate.
According to the invention, the substrate on which a film is formed is irradiated with light of a longer wavelength than the surface roughness Rmax of the substrate. By thus optimizing the wavelength of the irradiation light, the interference fringes can be obtained, and thus the film defects can be inspected.
Further, in the film defect inspection method of the invention, it is preferable that the substrate is irradiated with light of a wavelength of 500 nm or more when the surface roughness Rmax of the substrate is 0.5 xcexcm or more.
According to the invention, it is preferable that the substrate is irradiated with light of a wavelength of 500 nm or more especially when the surface roughness Rmax of the substrate is 0.5 xcexcm or more. Consequently, the interference fringes can be obtained with reliability, and the inspection of the film defects becomes possible.
Further, in the film defect inspection method of the invention, it is preferable that when the surface roughness Rmax of the substrate is 0.5 xcexcm or more, the substrate is irradiated with light of a wavelength beyond a little longer wavelength than the surface roughness Rmax.
According to the invention, in particular, when the surface roughness Rmax of the substrate is 0.5 xcexcm or more, the substrate is irradiated with light of a wavelength beyond a little longer wavelength than the surface roughness Rmax. Consequently, the interference fringes can be obtained with reliability, and the inspection of the film defects becomes possible.
Further, the invention provides a film defect inspection method for inspecting defects of a film formed on a substrate by a light interference method, comprising:
irradiating the substrate with light of a longer wavelength than a surface roughness Rz of the substrate.
According to the invention, the substrate on which a film is formed is irradiated with light of a longer wavelength than the surface roughness Rz of the substrate. By thus optimizing the wavelength of the irradiation light, interference fringes can be obtained, and the film defects can be inspected.
Further, in the film defect inspection method of the invention it is preferable that when the surface roughness Rz of the substrate is 0.5 xcexcm or more, the substrate is irradiated with light of a wavelength of 500 nm or more.
According to the invention, in particular, when the surface roughness Rz of the substrate is 0.5 xcexcm or more, the substrate is irradiated with light of a wavelength of 500 nm or more. Consequently, interference fringes can be obtained with reliability, and the inspection of film defects becomes possible.
Further, in the film defect inspection method of the invention it is preferable that when the surface roughness Rz of the substrate is 0.5 xcexcm or more, the substrate is irradiated with light of a wavelength beyond a little longer wavelength than the surface roughness Rz.
According to the invention, especially when the surface roughness Rz of the substrate is 0.5 xcexcm or more, the substrate is irradiated with light of a wavelength beyond a little longer wavelength than the surface roughness Rz. Consequently, the interference fringes can be obtained with reliability, and the inspection of film defects becomes possible.
Further, in the film defect inspection method of the invention, it is preferable that the substrate surface is subjected to a cutting work.
According to the invention, a film is formed on the substrate whose surface is relatively rough due to the cutting work. Such a substrate is irradiated with the foregoing optimized light. The interference fringes can also be obtained in this case, and the inspection of film defects becomes possible.
In the film defect inspection method of the invention, it is preferable that the substrate is electrically conductive, and on the substrate are formed an electric charge generation layer, and an electric charge transport layer or an undercoat layer, which constitute an electrophotographic photoreceptor along with the substrate.
According to the invention, specifically, the defects of the electric charge generation layer and electric charge transport layer or undercoat layer of the electrophotographic photoreceptor can be inspected.
Further, in the film defect inspection method of the invention, it is preferable that the electrophotographic photoreceptor is one for digital copiers or printers
According to the invention, it is possible to inspect the defects of the foregoing layers of the electrophotographic photoreceptor in which the layers are provided on the substrate having a relatively rough surface, that is, the electrophotographic photoreceptor to be mounted in a digital copier or printer.
Further, in the film defect inspection method of the invention, it is preferable that the substrate is irradiated with monochromatic light or indirect light, and the indirect light is light reflected from a reflector plate or light diffused by a diffusing plate.
According to the invention, by irradiation with monochromatic light, clearer interference fringes can be obtained. Therefore, the film defect inspection with high accuracy becomes possible. Further, by irradiation with indirect light, the interference fringes can be obtained over the wide range, and hence a reduction in inspection time can be achieved. Thus, film defects can be inspected with efficiency to improve productivity.
Further, in the film defect inspection method of the invention, it is preferable that the film defect inspection is an inspection of variations in film thickness or an inspection of foreign matters in the film.
According to the invention, it is possible to inspect the defects of variations in film thickness and inclusion of foreign matters by interference fringes.